**To Verify the Laws of Combination (Series) of Resistances Using a Metre Bridge**

**Aim**

To verify the laws of combination (series) of resistances using a metre bridge.

**Apparatus**

A metre bridge, a Leclanche cell (battery eliminator), a galvanometer, a resistance box,

a jockey, two resistance wires or two resistance coils known resistances, a set square, sand paper and connecting wires.

**Theory**

where R is the resistance from the resistance box in the left gap and l is the length of the metre

bridge wire from zero end upto balance point.

**Circuit diagram**

**Procedure**

1. Mark the two resistance coils as r_{1} and r_{2}.

2. To find r_{1} and r_{2} proceed same way as in Experiment 1. (If r_{1} and r_{2} are not known.)

3. Connect the two coils r_{1} and r_{2} in series as shown in figure in the right gap of metre bridge and find the resistance of this combination. Take at least three sets of observations.

4. Record your observations as follows.

**Observations**

Table for length (1) and unknown resistance (X)

**Calculations**

1. Calculation for r_{1} only, r_{2} r_{2}only, r_{1 }and r_{2} in series.

Same as in Experiment 1.

2. Calculation for verification of laws Experimental value of R_{s} = ……

Theoretical value of R_{s} = r_{1} + r_{2} = ……

Difference (if any) = ……

**Result**

Within limits of experimental error, experimental and theoretical values of Rs are same. Hence, law of resistances in series is verified.

**Precautions**

- The connections should be neat, clean and tight.
- Thick copper wires should be used for the connections after removing the insulations near their ends by rubbing with sand paper.
- Voltmeter and ammeter should be of proper range.
- A low resistance rheostat should be used.
- The key should be inserted only while taking observations to avoid heating of resistance (otherwise its resistance will increase).

## Comments by Paras